THE SRC-FAMILY PROTEIN-TYROSINE KINASE P59(HCK) IS LOCATED ON THE SECRETORY GRANULES IN HUMAN NEUTROPHILS AND TRANSLOCATES TOWARDS THE PHAGOSOME DURING CELL ACTIVATION

The src-family protein-tyrosine kinase p59(hck) is mainly expressed in neutrophils; however, its functional role in these cells is unknown. Several other src-family members are localized on secretory vesicles a nd have been proposed to regulate intracellular traffic. We have estab lished here the subcellular localization of p59(hck) in human neutroph ils. Immunoblotting of subcellular fractions showed that approx. 60 % of the p59(hck) per cell is localized on the secretory granules; the o ther 40 % is distributed equally between non-granular membranes and th e cytosol. Immunofluorescence of neutrophils and HL60 cells suggests t hat the p59(hck)-positive granules are azurophil granules. Granular p5 9(hck) is highly susceptible to degradation by an azurophil-granule pr oteinase. Different forms of p59(hck) occur in the three subcellular c ompartments: a 61 kDa form is mainly found in the granules, a 59 kDa f orm is predominant in the non-granular membranes, whereas cytosolic p5 9(hck) migrates as a doublet at 63 kDa. During the process of phagocyt osis-linked degranulation, induced by serum-opsonized zymosan in neutr ophils or HL60 cells, granular p59(hck) translocates towards the phago some. The subcellular localization of p59(hck) suggests that the enzym e could be involved in the regulation of the degranulation process.